The present invention relates generally to systems for generating microwave excited plasma discharges, and more particularly to systems for effectively cooling high power microwave plasma tubes.
In the copending application, use of liquid dimethyl polysiloxane as a coolant of high power, microwave (2450 MHz) excited plasmas useful as high intensity ultraviolet (UV), visible and infrared (IR) lamps was demonstrated. Liquid dimethyl polysiloxane used in coolant system structures of suitable configuration exhibited high UV and visible transmission, low microwave absorption at the desired microwave operating frequency, ability to withstand high cw or pulsed UV and visible fluences, non-toxicity and non-flammability, large IR absorption and desirable physical chemistry properties (low viscosity, low vapor pressure, large heat capacity, high thermal conductivity). The teachings of the copending application and background material presented therein are incorporated herein by reference.
Existing UV lamp systems that incorporate microwave excited plasmas mounted in a reflector assembly generally require large air cooling capacity (e.g., 240 cfm) and a.c. (60 Hz) power to the magnetrons. The present invention solves this deficiency in prior art structures by providing a coolant system in a reflector assembly for a microwave excited plasma incorporating liquid dimethyl polysiloxane as coolant. The cooling system provided by the invention obviates the need for large gas flow cooling capability for the plasma tube, can accommodate any reflector geometry (e.g. elliptical, circular, spherical, parabolic or involute), and allows higher (viz., about two times) power loadings to be accomplished for the plasmas.
It is therefore a principal object of the invention to provide a coolant system for high power microwave excited UV lamps utilizing liquid dimethyl polysiloxane in a reflector assembly capable of focusing output radiation.
It is another object of the invention to provide transverse or coaxial liquid cooling to a microwave excited plasma tube in a UV, visible or IR reflector assembly of any geometry.
These and other objects of the invention will become apparent as a detailed description of representative embodiments proceeds.